A slurry may refer to any suitable heterogeneous mixture of solid particles in a liquid. Illustrative, non-exclusive examples of slurries include dispersions, suspensions, and/or colloids. Slurries may include heterogeneous mixtures, in which the solid particles may be physically distributed within the liquid, but in which at least a portion of the solid particles may separate from the liquid naturally over time due to various spontaneous, or naturally occurring, separation mechanisms. Illustrative, non-exclusive examples of such separation mechanisms include settling, agglomeration, aggregation, precipitation, coalescence, sedimentation, creaming, and/or other separation processes that may be governed by gravitational, electrostatic, interfacial, and/or other naturally occurring forces.
However, for certain slurries, these spontaneous separation processes may be extremely slow and/or may proceed for a period of time, after which a separation rate may decrease significantly and/or separation may effectively cease. Additionally, slurries also may include heterogeneous mixtures, in which at least a portion of the solid particles may remain suspended within the liquid indefinitely due to electrostatic repulsion among the solid particles that may resist the above separation mechanisms. In addition, capillary forces between the liquid and the solid particles may further slow the separation process.
In a number of industrial processes, illustrative, non-exclusive examples of which include oil production, separation of hydrocarbons from oil sands, and/or dewatering of mine tailings, it may be desirable to separate at least a portion of the liquid component of the slurry from the solid particles. For certain slurry compositions, separation of the solid and liquid components of the slurry may be accomplished by making use of the above-described naturally occurring separation mechanisms. However, a separation rate obtained using these naturally occurring separation mechanisms may be significantly slower than a separation rate that may be desired and/or needed for efficient and/or economical operation of the separation process. In addition, natural separation of the solid and liquid components simply may not occur for other slurry compositions.
While a number of processes for separating the components of a mixture exist, these processes may not be effective and/or economical for separating slurry components. This may be due to a variety of factors, illustrative, non-exclusive examples of which may include the abrasive nature of some solid particles and the expense associated with designing and/or constructing valves and/or seals that may resist damage and/or wear due to slurry flow therethrough, the high viscosity of some slurries, and/or plugging of filtration apparatus by the solid particles.
As an illustrative, non-exclusive example, pressure-driven membrane filtration processes may be utilized to separate components of a mixture of solid particles and a liquid, or a solid-liquid mixture. These processes may include pressurizing a fluid that includes particulate material and contacting the fluid-particulate mixture with a first side of a porous surface that has a reduced pressure on a second side. Driven by the pressure differential across the porous surface, the liquid will flow therethrough. However, the solid components that are too large to pass through the porous surface will remain on the first side of the porous surface.
While such pressure-driven membrane filtration processes may be effective at separating the components of the solid-liquid mixture, they also have several limitations. As an illustrative, non-exclusive example, the porous surface may become plugged and/or the pores of the porous surface may become occluded due to the accumulation of solid particles on the first side of the porous surface, resulting in the formation of a filter cake. While this plugging may be reduced and/or eliminated through replacement of the porous surface with a new porous surface and/or by backflow through the filtration equipment, both of these processes may require that the filtration system be taken offline for a period, resulting in lost time and/or a quasi-batch separation process.
In addition to backflowing, the buildup of a filter cake may be reduced by flowing the solid-liquid mixture in a direction that is generally parallel to the porous surface. This parallel flow may result in shear forces that may erode the filter cake and/or substantially reduce formation. However, even when the formation of the filter cake is significantly reduced, the capillary forces between the liquid and the solid particles may prevent the separation process from proceeding at the desired separation rate.